Mattress for a man who has a lower back condition and arthritis?

Hi,
I am 57 yrs, 183cm tall and weigh 84kg, my wife is 51yrs, 155cm and 72kg . We both sleep on our back and side.
I have a lower back condition a result of trauma caused during my years in the military, I also have arthritis which is aggravated by our current mattress. My wife also suffers but to a lesser degree.
Our priorities in mattress selection is purely that of comfort, to be able to have an undisturbed painfree nights sleep and awake with the flexibility with which we went to bed.
Of course cost is always a consideration and as such do not want to pay more than we have to to find a mattress that meets our needs.
Yours in desperation,